The present invention relates to endless conveyor belts and, in particular, to belt systems driven directly by an endless chain in a spiral pattern.
It is known to construct a metal conveyor belt from a plurality of loosely linked rods (U.S. Pat. No. 4,078,655). Such a belt can turn in different directions and is used for moving various products such as baked goods or other manufactured goods which require a transit time to allow cooling, drying, etc.
It has been proposed to turn such a belt 180.degree. while maintaining the rods horizontal. Such turning is accomplished by routing an endless chain around a semicircular arc. Under these circumstances the belt can directly engage the endless chain and be driven thereby (U.S. Pat. No. 3,270,863).
It has been found difficult to route conveyor belts in a spiral pattern. For example, if belts of the foregoing type (loosely coupled rods) are driven by a chain, intermediating devices have been needed to create an appropriate grip between the chain and the belt. In some instances, a plurality of cleats were welded to the chain to ensure a grasp between chain and belt (U.S. Pat. No. 3,682,295). Such structure adds additional weight, however, and results in a more elaborate product involving large amounts of labor to weld many cleats to a chain.
It is known to drive a conveyor belt in a spiral path by providing a central cage that turns as a whole, similar to a capstan. The conveyor belt is wound around this cage to turn with it. Because of the nature of this design, slippage between the belt and cage is expected. This unfortunately increases wear, vibration and noise. Because of the unpredictable nature of the slip a variable speed drive motor is necessary to produce a predictable conveyor speed. Another disadvantage with this type of structure is that the rotating weight of the turning structure is high. Furthermore, central reinforcements are necessary in the cage and as a result, there is no open space in the center of the cage. This precludes the possibility of mounting accessory components in the center of the cage (or building the conveyor around an obstruction such as a building column).
It is also known to replace the turning central cage with a plurality of spaced spindles arranged in a circle and rotating synchronously. Each of these vertical spindles has a friction wheel for directly engaging the conveyor belt. A disadvantage of this type of system is the necessity of having many rotating shafts with the spaces between the shafts nevertheless non-driving. Consequently, the operation of the latter system tends to be uneven and rough. The inner perimeter of the spindle-type of system is not a smooth circle but a multisided polygon. This means the belt actually travels in a straight line between drive rings, periodically turning around a spindle which has a radius far less than the recommended radius that the belt is designed for. This instantaneous belt radius creates unusually high operating tension in the belt and effectively reduces its life. Also, this uneven motion produces belt flexing at each drive spindle that disorients the product being conveyed. Another disadvantage with the spindle type of systems is that they often require an outside guide to hold the conveyor belt against the inner driving apparatus. This apparatus increases the assembly size as well as increasing friction and wear.
Accordingly, there is a need for an improved conveyor system wherein a belt may be circulated spirally and driven by a spiralled chain, wherein the belt is arranged to close on the spiral in a simple and efficient manner.